This NYC-based project will evaluate the performance (sensitivity and specificity), cost-effectiveness, and feasibility of using a new fourth generation HIV test which detects both IgM antibody and HIV p24 antigen. Populations of persons attending a pair of sexually transmitted disease clinics, two bath houses catering to men who have sex with men (MSM), and a busy urban hospital Emergency Department will be offered screening with three different HIV test types (rapid point of care test, pooled nucleic acid amplification testing, and fourth generation test), and a longitudinal study of men attending bathhouses will be conducted to evaluate repeat testing as an AHI detection strategy in high risk MSM. Targeted hepatitis C screening and universal hepatitis B Screening will be done in the STD and MSM populations to examine the feasibility of operationalizing new, expanded guidelines for hepatitis B screening and public health management. Traditional (provider referral) and internet partner notification approaches will be evaluated; phylogenetic analysis of HIV will be done to measure the degree of relatedness between HIV from different case-patients and partners. Phylogenetic and antiviral resistance patterns will be used to inform and elucidate the sexual networks described by traditional partner notification activities.